Two-stage distillation of orthosubstituted ring compounds



D. B. LUTEN, JR., ETAL STAGE DISTILLTION OF ORTHO-SUBSTITUTED RINGCOMPOUNDS TNO- lFiled May 29, 1941 lnvenforst Dane B. LuTen, .Tf-2.

oei. 22, 1946.

Patented Oct. 22, 1946 TWO-STAGE DSTILLATION OF ORTHO- SUBSTITUTED RINGCOMPOUNDS Daniel B. Luten,` Jr., and Aldo De Benedctis, Berkeley,Calif., assignors to Shell Development Company, San Francisco, Calif., acorporation of Delaware Application May 29, 1941, Serial No. 395,784

8 Claims. 1

Thspresent invention relates to a process for separating polar organiccompounds. More particularly, it relates to a process wherein mixturesof poly-substituted conjugated ring compounds with themselves or otherorganic compounds are separated by distillation under controlledpressures.

It is the object of our invention to separate certain organic compoundsby distillation, whose separation by this method heretofore has beenconsidered impossible due to their similar vapor pressures under normalcircumstances.

Our invention comprises distilling mixtures of associated polarcompounds differing in extent to which the polar radicals are flanked bynonpolar radicals such as mixtures of poly-substi tuted conjugated ringcompounds of the type described below at a given pressure to produce afraction having narrow boiling range and then further distilling thenarrow 'fraction underl substantially different pressures to produce atleast two fractions rich in different components of the mixture.

Our process is applicable to the separation of other organic compoundsfrom compounds of the following type: derivatives of benzene, pyridine,naphthalene, quinoline and isoquinoline, which contain not more than onepolar grouping selected from NH2, =N, COOH and OI-I, and which furthercontain in ortho position to 'the polar group at least one non-polarhydrocarbon radical such as methyl, ethyl, propyl, isopropyl, primary,secondary and tertiary butyl, amyl, hexyl, cyclohexyl, methylcyclohexyl, phenyl, tolyl, xylyl, phenyl methyl, phenyl ethyl, naphthyl,tetryl, etc.

We have discovered that when mixtures of one or several of these orthoconjugated ring com pounds with other organic compounds (the latterincluding compounds which diier from the former only in that thehydrocarbon radical is in a position other than ortho to the polargroup) are distilled under a given pressure to produce a narrow boilingfraction, e. g. of less than 10 C. boiling range and containing at leastone ortho and some other compound, it is necessary only to redistill thefraction so produced under substantially different pressure to get aclean separation between the ortho-substituted compounds and the othercompounds present in this fraction. Our process is based upon ourdiscovery that certain ortho-substituted derivatives of benzene,naphthalene, pyridine, quinoline and isoquinoline, tend to havesignificantly lower heats of vaporization than the corresponding meta orpara derivativesor other derivatives of approximately the same molecularweight. Thus, due to the lower heat of vaporization, ortho compoundshave a lower rate of change of vapor pressure with temperature thannon-ortho compounds, and it follows that there will be a higher rate ofchange of boiling point Vfor ortho compounds with pressure than withnon-ortho compounds. This abnormal decrease in vapor pressure exhibitedby mono-ortho compounds under reduced pressure is even more pronouncedwhen two hydrocarbon radicals are ortho to the polar group, and thusseparations can be obtained between diortho and mono-ortho compoundsusing the same principle. For example, by our process we can readilyseparate Z-ethyl, 5-methyl phenol (mono-ortho) from 2,4,6-trimethylphenol (di-ortho) both of which boil under normal conditions at about220 C. by distilling at substantially atmospheric pressures a mixture ofacid oils containing tliem to produce a fraction having a boiling rangefrom below to above 220 C., for example, about 218- 222 C., andsubsequently redistilling this fraction at a reduced pressure of about 5mm. Under these conditions the ZA-trimethyl phenol is concentrated inthe top product while the 2 -ethy1, 5-methyl phenol is concentrated inthe bottom product. In the same manner meta cresol can be separated from2,6dimethyl phenol, etc.

Examples of other separations according to our process follow:2,4,6-trimethyl phenol may be separated from mixtures with otherphenols; 2,6- dimethyl phenol can be separated from cresols; 3,5- and3,4-dimethyl phenol can be separated from their mixtures; S-methyl,5-ethyl phenol from mixtures of phenols; beta-gamma picoline can beseparated from 2,6-lutidine; metaand para-ethyl phenols from theirmixtures, etc.

The separation may be carried out either batchwise or continuously. Inthe former process an initial material generally having a wide boilingrange, e. g. more than 10 C. and containing ortho-substituted compoundsand other compounds, is distilled to produce a fraction having a narrowboiling range, usually not greater than about 10 C., and subsequentlythis narrow fraction is redistilled at a substantially differentpressure to separate the ortho compounds from the nonortho compounds.

In the continuous process the initial material is continuously fed to afractionating column, from which is withdrawn continuously a fraction ofnarrow boiling point containing ortho and non-ortho compounds,` whichfraction is fed toa second column operated under a different pres- 3sure from which is continuously withdrawn the ortho compoundsconcentrated in one fraction while the non-ortho compounds areconcentrated in the other. The continuous process is advantageous whenit is desired to process large quantities of material.

Still another way to carry out our process may be termedbatch-continuous. In this process a broad fraction is charged to a batchstill from which is obtained an overhead product of narrow butcontinuously changing boiling range. This stream is introduced, asrapidly as it is obtained, into a continuous column operating at adifferent pressure. The top and bottom products from the continuouscolumn are predominantly di-ortho and non-ortho substituted compounds,respectively, if the pressure is diminished for the second distillation,and non-ortho and di-ortho substituted compounds, respectively, if thepressure is increased for the second distillation. The mono-orthocompounds may be obtained in either the top or bottom product byadjusting the reflux and reboiling ratios in the continuous column.

Although we may carry out our initia1 distillation at any suitablepressure below or above atmospheric and our subsequent distillation atanother pressure either above or below atmospheric, it is generally mostconvenient to make the initial distillation at pressures at or nearatmospheric, and carry out the subsequent distillation at reducedpressure, although sometimes we may prefer to carry out the initialdistillation at reduced pressure and the subsequent distillation atincreased pressures.

The maximum pressure which we apply depends upon the thermal stabilityof the mixture being separated. In general, we prefer to use pressuresbelow those associated with temperatures at which decomposition occurs.The minimum pressure is limited solely by the apparatus at hand, but ingeneral we prefer to carry out the low pressure distillation atpressures less than mm. Since the ease of separation depends upon thedifference between the pressure used in the different distillations, itis therefore generally desirable that this difference be made as largeas is convenient and economical, always considering the pressure at thedecomposition temperature as the upper limit.

Whether the ortho or non-ortho compound accumulates in the top or thebottom fraction depends upon the pressure relationship. In general, thelower the pressure, the more enhanced is the relative volatilityaccording to the following series:

Di-ortho compounds monoortho compounds other compounds. Thus, when theinitial distillation is made at higher pressures and the subsequentdistillation at lower pressure, the di-ortho or ortho compounds appearin the top fraction While the other compounds appear in the bottomproduct.

This relationship is reversed when the initial distillation is made atlower pressure and the subsequent distillation at higher pressure. Inthis case the non-ortho compounds are concentrated in the top fractionwhile the ortho or di-ortho compounds are concentrated in the bottomfraction.

The present invention may be better understood from a consideration ofthe figure, which is a liow diagram representing one embodiment thereof,wherein a relatively wide boiling phe- A 1y high so that a large part ofnolic mixture containing ortho-substituted phenols andnon-ortho-substituted phenols is continuously fed via line I tofractionating column 2 equipped with reboiler 3. The heat input tocolumn 2 is so regulated that a portion of the lower boiling componentsof the mixture passes overhead via line 4, condenses in condenser 5 andcollects in accumulator 6, whence a portion is returned as reilux tocolumn 2 via line l, while the remaining low boiling components arewithdrawn via line passing to storage not shown. The bottom productcontaining a major portion of the ortho-substituted phenols along withother non-ortho-substituted phenols and heavier boiling constituents,passes via line 9 to column I0 equipped with reboiler II. The heat inputto column vIf) is so regulated that the bulk of orthosubstituted phenolspasses overhead while the bulk of the remaining higher boilingcomponents is withdrawn via line I2, passing to storage not shown. Therelatively narrow boiling ortho-substituted phenols, along with otherquantities of non-ortho-substituted phenols, pass overhead via line I3,condense in condenser I 4 and collect in accumulator I5, whence aportion is returned to column I0 as reilux via line I6. The remainder istreated as subsequently described. Both column 2 and column I0 areoperated at substantially atmospheric pressure and thus exemplify higherpressure distillation for the primary purpose of producing a relativelynarrow fraction, which latter passes via line I 'I to low pressurefractionation column I8 equipped with reboiler I8. In this distillation,the non-ortho-substituent phenols are withdrawn as bottom product vialine 20, while the ortho-substituted phenols pass overhead via line ZIto condenser 22 and collect in accumulator 23, whence a portion isreturned as reilux via line 24 to column I8. The remainingortho-substituted phenols are withdrawn via line 25, passing to storagenot shown. Column I8 is maintained under vacuum by exhauster 25connected to accumulator 23 via line 2l. Exhaust gases pass fromexhauster 26 via line 28 and may be disposed of as desired.

For purposes of simplicity, by passes, heat exchanges, auxiliary pumpsand control means, the proper placement of which is evident to thoseskilled in the art, have been omitted.

Eample I alkyl phenols containsure, however, the rst fraction, amountingto about 35% of the charge, contained 60% 2,6-dimethyl phenol togetherwith 30% o-cresol and small amounts of the other phenols. Thisconcentration of 2,6-dimethyl phenol was sufcientthe substancecrystallized out of solution and could readily be isolated.

The second portion of the original mixture was first fractionated at 10mm. pressure to give a Example II A, fraction .of petroleum alkylphenols boiling from about 210 C. to about 230 C. and consisting mostlyof methyl ethyl phenols containing one ortho substituent and variouspolymethyl phenols, including mesitol `(2,4,6-trirnethyl phenol, boilingpoint 220 C.) and symmetrical xylenol (3j-dimethyl phenol, boiling point219.5 CJ, was fractionally distilled through a column equivalent toabout ten theoretical plates and operating at about mm. pressure and areflux ratio of 10: 1, the `distillate being recovered in tenapproximately equal fractions. One of the 10% fractions obtained in theearlier part of the distillationhad a boiling point of 216 C. whileanother fraction obtained in a later stage had a boiling point of 224 C.Each of these was reiractionated again into `10% portions at atmosphericpressure in a column equivalent to about 12-15` theoretical plates` andoperated at 10:1 reflux ratio. While this treatment was not sufficientto resultl in the separation of any pure phenols, the highest boilingfractions of the 216 C. cut contained sufficient mesitol so that itsconcentration exceeded its solubility in liquid alkyl phenols (about at20, C.) and it crystallized out of solution in` part. On the other handthe lowest boiling fractions obtainedV from` the224 C. fractioncontained symmetrical xylenol in sufficient concentration (itssolubility in liquid alkyl phenols is about 35% at 20 C.) so that italso crystallized out of solution in part.

Thus, in the vacuum fractionation mesitol, a di-.ortho substitutedphenol, was segregated with material normally boiling at 216 C. whilesymmetrical xylenol, a non-ortho substituted phenol, was segregated withmaterial normally boiling at 224 C.; upon refractionation at atmosphericpressure the mesitol was separated from the 216 C. material as a higherboiling substance while the symmetrical Xylenol was separated from the224 C. fraction as a lower boiling substance.

We claim as our invention:

1. in a process for separating an ortho substituted conjugated ringcompound from other substituted conjugated ring compounds in anassociated mixture thereof having a relatively wide boiling range, saidortho compound and at least some of said other compounds havingsubstantially identical boiling points at a given pressure and having anucleus selected from the group consisting of benzene, pyridine,naphthalene, and quinoline and containing a single polar group selectedfrom the class consisting of -NH2, -COOl-I, -OI-I, and :2N- the orthopositions to said polar group in said ortho compound being occupied byat least one no-n-polar hydrocarbon radical, While said other compoundsare differently substituted, the steps comprising: fractionallydistilling said mixture under said given pressure to produce a fractionhaving a relatively narrow boiling range at said given pressure, saidfraction containing at least a portion of said ortho and said some ofsaid other compounds of substantially identical boiling points at saidgiven pressure;` and further fractionally distilling said fraction undera pressure substantially increased above. said given pressure to producean overhead and a bottom product, one of which is rich in saidortho-substituted compound and the other is rich in said some of saidother compounds.

2. In a process for separating an ortho phenol from other phenols in amixture thereof` having a relatively wide boiling range, said orthophenol and at least some of Said other phenols having substantiallyidentical boiling points at a given pressure, the ortho position to thehydroxyl group in said ortho phenol being occupied by at least onenon-polar hydrocarbon radical, while the ortho positions in said otherphenols are diiferently substituted, the steps comprising: fractionall-ydistilling saidr mixture under said given pressure to produce a fractionhaving a relatively narrow boiling range, said fraction containing atleast a portion of said ortho and said some of said other phenols havingsubstantially identical boiling points at said given pressure; andfurther fractionally distilling said fraction under a pressuresubstantially increased above said given pressure to produce an overheadand a bottom product, one of which is rich in said ortho phenol and theother of which is rich in said some of said other phenols.

3. In a process for separating an ortho phenol from` other phenols in amixture thereof having a relatively wide boiling range, said orthophenol and at least somefof said other phenols having substantiallyidentical boiling points under atmospheric pressure, the ortho positionsto the hydroxy group in said ortho phenol being occupied by atleast onenon-polar hydrocarbon radical, while the ortho positions in said otherphenols are differently substituted, the steps comprising: fractionallydistilling said mixture under substantially atmospheric pressure toproduce a fraction having a relatively narrow boiling range underatmospheric pressure, said fraction containing at least a portion ofsaid ortho phenols and said some of said other phenols; and furtherfractionally distilling said fraction under a pressure substantiallyabove atmospheric pressure to produce a bottom product rich in saidortho phenol and an overhead fraction rich in said some of said otherphenols.

4. In a process for separating 2,4,6-trimethyl phenol from a mixture ofphenols having a relatively wide boiling range, at least a portion ofthe other phenols in said mixture having a boiling point substantiallyidentical with that of 2,4,6- trimethyl phenol at a given pressure, thesteps comprising: fractionally distilling said mixture under said givenpressure to produce a fraction having a relatively narrow boiling range,said fraction containing at least a portion of said 2,4,6- trimethylphenol and of said portion of the other phenols having the substantiallyidentical boiling temperature at said given pressure; and furtherfractionally distilling said fraction under a pressure substantiallydifferent from said given pressure to produce an overhead and a bottomproduct, one of which is rich in 2,4,6-trimethyl phenol, and the otherof which is rich in the phenols of said portion of said phenols.

5. In a process for separating 2,6-dimethyl phenol from other alkylphenols in a mixture thereof having a relatively Wide boiling range, at

least a portion of said alkyl phenols having a boiling pointsubstantially identical with that of 2,6-dimethyl phenol under a givenpressure, the steps comprising: fractionally distilling said mixtureunder said given pressure to produce a iraction having a relativelynarrow boiling range, said fraction containing at least a portion ofsaid 2,6-dimethyl phenol and of said other alkyl phenols having thesubstantially identical boiling point at said given pressure; andfurther iractionally distilling said fraction under a pressuresubstantially different from said given pressure to produce an overheadand a bottom product, one of which is rich in 2,6-dimethyl phenol andthe other of which is rich in other alkyl phenols.

6. In a process for separating an ortho substituted conjugated ringcompound from other substituted conjugated ring compounds in anassociated mixture thereof having a relatively wide boiling range, saidortho compound and at least some of said other compounds havingsubstantially identical boiling points at a given subatmosphericpressure and having a nucleus selected from the group consisting ofbenzene, pyridine, naphthalene, and quinoline and containing a singiepolar group selected from the class consisting of -NH2, -COOI-I, -OH,and =N-, the ortho positions to said polar group in said ortho compoundbeing occupied by at least one non-polar hydrocarbon radical, while saidother compounds are dilerently substituted, the steps comprising:fractionally distilling said mixture under said given subatmosphericpressure to produce a fraction having a relatively narrow boiling rangeat said subatmospheric pressure, said fraction containing at least aportion of said ortho and said some of said other compounds ofsubstantially identical boiling points at said given subatmosphericpressure; and further fractionally distilling said fraction undersubstantially atmospheric pressure to produce an overhead and a bottomproduct, one of which is rich in said orthosubstituted compound and theother is rich in said some of said other compounds.

'7. In a process for separating an ortho substituted conjugated ringcompound from other substituted conjugated ring compounds in anassociated mixture thereof having a relatively wide boiling range, saidcompounds having a nucleus selected from the group consisting ofbenzene, pyridine, naphthalene and quinoline and containing a singlepolar group selected from the class consisting of -NH2, -COO'I-I, -OH,and =N-, said ortho compound containing at least one hydrocarbon radicalin ortho position to said polar group while said other compounds aredifferently substituted, said ortho compound and one of said othercompounds having substantially identical boiling points at some givenpressure, the steps comprising: batch distilling said mixture under saidgiven pressure to produce an overhead stream having a relatively narrowbut continuously changing boiling range, which, over a period of time,includes the boiling temperature at said given pressure of said orthocompound, thereby producing a fraction containing at least a portion ofsaid ortho compound and of said other compound of substantiallyidentical boiling point at said given pressure; and continuously feedingsaid fraction in the form of said stream to a continuous distillationcolumn wherein it is refractionated at a pressure substantiallyincreased above said given pressure to produce an overhead and a bottomproduct, one of which is rich in said ortho compound and the other isrich in said one of said other compounds.

8. In a process for separating an ortho substituted conjugated ringcompound from other substituted conjugated ring compounds in anassociated mixture thereof having a relatively wide boiling range, saidcompounds having a nucleus selected from the group consisting ofbenzene, pyridine, naphthalene and quinoline and containing a singlepolar group selected from the class consisting of -NH2, -COOH, -OH, and=N-, said ortho compound containing at least one hydrocarbon radical inortho position to said polar group while said other compounds arediierently substituted, said ortho compound and one of said othercompounds having substantially identical boiling points at some givenpressure, the steps comprising: batch distilling said mixture under saidgiven pressure to produce an overhead stream having a relatively narrowbut continuously changing boiling range, which, over a period of time,includes the boiling temperature at said given pressure of said orthocompound, thereby producing a fraction containing at least a portion ofsaid ortho compound and of said other compound of substantiallyidentical boiling point at said given pressure; and continuously feedingsaid fraction in the form of said stream to a continuous distillationcolumn wherein it is refractionated at a pressure substantiallydifferent from said given pressure to produce an overhead and a bottomproduct, one of which is rich in said ortho compound and the other isrich in said one of said other compounds.

DANIEL B. LUTEN, JR. ALDO DE BENEDICTIS.

